Textile yarn cores, i.e., yarn carriers or bobbins, are employed in the textile industry for winding and supporting yarn packages. In the package forming process, a moving yarn line is strung up onto a rapidly rotating empty core. The moving yarn line is usually held by an aspirator gun and the yarn line brought into tangential contact with the rotating empty core. Typically, a start-up groove is provided in the surface of the core, normally adjacent one end of the core. The yarn line is directed into the groove which grips and breaks the yarn line thereby initiating the wind-up process.
Multiple width start-up grooves in yarn cores have been provided in an effort to improve the yarn pick up propensities of the yarn groove. In the multiple width pick up grooves, one longitudinal, i.e., lengthwise, portion of the groove is relatively wide while an adjacent longitudinal portion is relatively narrow. The core is rotated so that the wide portion of the groove forms the leading portion; the narrow portion of the groove forms the trailing portion. The transition portion of the groove then forms a "nip" for gripping and catching of the yarn.
A textile core having such a double width groove and the process for forming it are disclosed in U.S. Pat. No. 3,103,305 to Heatherly. The grooves formed according to the disclosure of this patent have a generally V shaped cross-section with the sides of the groove being curved convexly inwardly towards each other. This groove configuration is said to permit the yarn to find its proper maximum position for sliding through the wide, lead-in portion of the groove while acting with maximum efficiency to catch, hold and sever the yarn as it is pulled into the nip while raising to a higher level in the narrow portion of the groove.
Universal pick up grooves for textile cores are disclosed in U.S. Pat. No. 4,369,933 to Bedenbaugh and U.S. Pat. No. 4,371,130 to Case. The pick-up grooves described in these patents include wide lead-in portions and adjacent narrow gripping portions. Two wide lead-in longitudinal groove portions are provided, one on each end of the narrow longitudinal portion of the pick-up groove so that the tube can be rotated in either direction while providing the wide, lead-in portion of the groove at the leading edge of the groove. The disclosure of these patents is hereby incorporated herein by reference.
Textile cores having a double taper or compound start-up groove are disclosed in U.S. Pat. No. 3,717,291 to Adams, et al. which is hereby incorporated by reference. The compound angle start-up groove is advantageously formed in the core using a compound angle cutting blade. In transverse cross-section, the compound angle cutting blade is defined by a narrow angle portion at the cutting tip of the blade and a wider angle portion spaced from the cutting tip. The resultant double taper groove in the yarn tube is wider and has a greater angle taper adjacent the surface of the tube, and is narrower, with a narrower taper at the bottom of the groove. A "pinch point" for the incoming yarn line is formed by the narrow tapering portion of the groove at the bottom of the groove.
In practice, the double-taper blades employed in the above-described Adams, et al. patent are typically ground on an abrasive stone-type grinder to achieve the proper tapers. The blade manufacturing process is relatively complicated and time consuming. In addition, care must be exercised during the grinding process in order not to adversely affect the temper of the metal of the grooving blade.
In the textile industry, yarn manufacturing and wind-up speeds having continually increased. Moreover, in many cases, yarn properties including yarn strengths have increased. As yarn manufacturing speeds have increased, the need for improved gripping action by the start-up groove in the textile cores has also increased. Moreover, in the case of high strength yarns, the gripping action of the start up groove must preferably be great enough that the yarn line can be readily gripped and severed. However, it has been found that conventionally formed start-up grooves in textile yarn cores do not always reliably and repeatably perform these functions, particularly when used with different sized yarns and yarns of different strengths.